Key Points
- Postherpetic neuralgia (PHN) is a painful aftermath of Herpes zoster (HZ, “shingles”). Acute HZ occurs when dormant varicella zoster virus is reactivated in ganglia and travels down sensory nerves to infect the skin in the involved dermatome.
- Common sites for shingles outbreaks are the thorax and face, usually in the ophthalmic division of the trigeminal nerve.
- Zoster can occur without a rash during the early phase; the absence of a rash and vesicles does not signify that the pain is not due to zoster (zoster sine herpete).
- The most important risk factors for PHN are older age (>60) and severe acute pain with acute shingles.
- PHN occurs following shingles in 5-15% of patients but occurs ~3x more often among those over age 60.
- Being immunocompromised raises the risk of having HZ and then PHN.
- Patients with PHN commonly describe a constant generally burning pain, and intermittent pain with lancinating or shooting quality. Brush-induced allodynia is observed in nearly 90% of cases.
- All persons 60 years and older should receive a zoster vaccination.
- In the Shingles Prevention Study, zoster vaccine reduced the incidence of PHN by 66.5%.
- Lifetime risk of developing acute HZ is as high as 40% - 50% of those over 50 years and 80% of those over 80.
- Immunizing children against chicken pox prevents HZ in later life.
- Oral acyclovir, famciclovir, and valacyclovir reduce acute pain and the duration of chronic pain in older patients who have HZ and are treated within 72 hours of rash onset, but even optimally treated patients can develop PHN.
Diagnosis and Assessment of Disease
- Differentiating HZ from Herpes simplex virus (HSV) infection is difficult;
- HZ should be diagnosed using laboratory diagnostic testing.
- Usually, HSV is found around the mouth and genitals and not on the trunk.
- Available diagnostic tests include viral culture, immunofluorescence antigen (IFA) or enzyme immunoassay (EIA) antigen detection, PCR, and serology.
